The actor added more seriously: "For me what was fascinating was that I had met him before and he was so nice, so I thought, 'What was going on, what can we get at?' And what I found was this incredible vulnerability, and his strength comes from an engine of vulnerability.

"He is a man that I admire because he is not afraid to show that, and I think what is underneath is what you see in this performance. In this performance is a man who's struggling deeply. The truth of who he is comes out in so many ways and in some extraordinary scenes. He's extraordinary in Prisoners."

"Working with him, we improvised a lot, he loves improv and so do I," he said. "We would throw things back and forth at each other. We were questioning and trying to discover our characters together, particularly at the beginning."

He went on to say: "And those few scenes we did at the beginning, and then particularly at the middle and end, we could both feel an evolution. He was a real guide for me, in what I was trying to figure out about Detective Loki, and I hope vice-versa. But it was really really fun.

"With a subject matter like this, which can seem not that way, it was incredibly fun acting. It was invigorating and enervating and you can see that his energy is like that. What I would say about Hugh is that I don't think he's always 'the nice guy', I just think he's a really, really good man."

Prisoners opens on Friday (September 20) in the US and on September 27 in the UK.